The present invention relates to contouring the groove of and in a pilger type roll particularly for a cold pilger rolling mill; and more particularly, to cutting and grinding the peripheral and cross-sectional contours of the groove by means of a grinding wheel or disk whose position and orientation is varied as grinding progresses.
The German Pat. No. 1,179,438 discloses equipment for grinding and milling a contour groove in the periphery of a roll using a rotating grinding disk which is tuned on a circle whose radius corresponds to the cross-sectional radius of the groove to be grinded, the axis of turning or pivoting extends transversely to the axis of rotation of the disk. In other words, the disk's periphery is moved over a circle in a plane defined by the axes of the disk and the roll. The points of contact between disk and roll is, however, not necessarily located in that same plane so that the resulting contour of the groove is somewhat distorted. The distortion depends on the diameter of the grinding wheel and the degree of wear thereof. In other words, a groove ground with a new wheel differs from the groove ground with a worn wheel, other conditions being the same. Of course, one could modify the control of the wheel's motion to compensate the progressing wear and resulting contour changes. However, it turns out that this correction is possible only as to the outer edges and the bottom of the groove, but not for the in-between areas. The control is provided, for example, by means of cams as shown, e.g. in German printed patent application No. 1,813,281.
In accordance with recent research results, it is necessary to define and to establish the effective groove of a pilger roll and its surface contour to a very high degree of accuracy in order to avoid fractures in and of the rolling mandrel or even of the rolls themselves. It has to be stated that we do not believe that any of the known methods for making the effective groove and its contour in a pilger roll are capable of accurately duplicating particular predetermined contours, having been, e.g. calculated in accordance with particular requirements and conditions for rolling particular hollows. Rather, deviations seem to be inevitable being the larger the larger the diameter reduction and inclination angle of the groove. The main reason seems to be that groove contour varies peripherally, i.e. azimuthally, which, in turn, makes it inevitable that the point of engagement between roll and grinding disk is outside of the plane defined by roll and disk axes. The distance of this point of engagement from that plane varies along the periphery and the advance angle of the groove.